Postinjury multiple organ failure is the net result of the dysfunctional immune response to injury characterized by an early hyperactive innate system. Acute lung injury (ALI) is the first clinical manifestation of organ failure, followed by renal and hepatic dysfunction. The gut has been invoked as the motor of MOF, and mesenteric lymph is recognized as the mechanistic link between splanchnic ischemia and distant organ dysfunction. But the specific mediators remain to be defined. Current evidence suggests the lipid fraction of post-shock mesenteric lymph (PSML) is central in the etiology of ALI. Specifically, our recent work indicates that 5-lipoxygenase (5-LO) products are essential, but proteins may have an important role. Elucidating these mediators is critical In translating our current knowledge to new therapeutic strategies at the bedside. Our specific research aims (abbreviated) are: 1) to determine if 5-lipoxygenase activity is necessary for PSML to provoke acute lung injury by examining a) mesenteric lymph diversion (MLD) in rats, b) pretreatment of rats with 5-LO inhibitors, c) knock out mice, d) 5-LO metabolites in BALF and pleural fluid of severely injured patients with ALI / ARDS; 2) to determine if T/HS activates 5-LO in the gut, thereby producing metabolites in PSML that mediate ALI by a) infusing rat PSML into naive rats from donor rats, pretreatedt with 5-LO inhibitors, monitoring for increases in 5-LO metabolites and ALI, b) incubating PMNs, HMVECs, alveolar macrophages, and type II pneumocytes with PSML and LTB4/ LTC4 receptor antagonists to produce proinflammatory activation, c) examining 5-LO metabolites in PSML following T/HS in rats, d) examining 5-LO metabolites in the mesenteric lymph of severely injured patients; and 3) to determine if T/HS activates 5-lipoxygenase in the lung by a) infusing isotope labeled (d8)AA into MLD T/HS rat lung to generate (d8)LTB{4}and produce ALI, b) cross-transfusing PSML from T/HS rats, pretreated with a PLA{2} inhibitor (to eliminate AA) or 5-LO inhibitor, into naive rats and measuring 5-LO metabolites in BALF and assessing for ALI, c) locating 5-LO pathway components in the lung versus infiltrating hematological cells (PMNs and platelets) following T/HS +/- MLD, d) determining if elevated alpha-enolase, elevated major urinary protein, or the depletion of antiproteases in PSML stimulates 5-LO activity in cultured PMNs, HMVECs, alveolar macrophages and type II pneumocytes, e) proteomics analysis of human lymph to identify relevant lipid carriers and 5-LO activators.